1. Field of the Invention
This invention relates to a fabric for use as the mesh layer of a batt-on-mesh papermakers' felt and more particularly, to a papermakers' felt comprising a fibrous batt attached to the mesh fabric layer by a needling process. The fabric comprises a multifilament yarn in the cross-machine direction, this multifilament yarn having a polyurethane coating thereon.
2. Description of the Prior Art
In general, press felts are used in papermaking machines to support the moist, freshly formed paper web as it encounters a variety of rolls which serve to extract water from the moist paper web. In addition to serving as a support for the paper web, the press felt serves as a receptacle for the water removed from the paper sheet.
The ideal felt should have a surface that is fine enough to produce a smooth finish and minimize marking of the sheet of paper being produced. It should also be open enough to allow water to drain through it without significant back-up. Additionally, it should be tough and strong enough to provide good stability, wear-resistance, and felt life.
Batt-on-base needled felts which consist of a batt or fleece of loosely associated non-woven fibers needled to a woven base fabric are well known to the art and possess several of the desired characteristics. Because of their relatively high drainage characteristics, these felts have been used extensively throughout the papermaking industry.
However, one problem encountered with the batt-on-base needled felts is that of excessive wear due to the abrasive action of the press rolls, felt rolls, conditioning equipment, and abrasive contaminants. These prior art felts have relatively low stability and resistance to wear and abrasion. These felts are plagued by distortion and have far shorter service lives than is desirable.
The newer batt-on-mesh felts utilize high strength twisted multifilament yarns or monofilaments. The mesh base not only has greater open area between machine and cross-machine yarns, but also resists compaction to a greater degree than the spun yarn base. However, these yarns still do not possess satisfactory felt life, having the disadvantage of reduced retention of the batt fibers and lower abrasion resistance of the mesh under certain conditions due to fibrillation of the filament surface.
In recent years, the speeds of papermaking operations have increased to the point that greater roll pressures have been necessitated, causing an increase in the tendency of felt to wear due to abrasion. In an effort to counteract the effects of the increased abrasion on the felts, particularly the mesh layer of these felts, a variety of materials have been used in the manufacture of the mesh fabric. Recently, thermoplastic monofilaments of nylon and polyester have been utilized.
Bond, U.S. Pat. No. 4,370,375, discloses a polyamide monofilament which exhibits resistance to abrasive forces applied transversely to the longitudinal dimension of the monofilament. The disclosure provides for an oriented polyamide monofilament having a diameter of about 3-30 mils and comprising filament-forming polyamide and about 3-10 weight percent, based on the total weight of the monofilament, of molybdenun disulfide. Fleischer, U.S. Pat. No. 4,093,512, discloses a papermakers' belt comprising ultra high modulous load bearing yarns which may be resin coated, or wrapped and then resin coated, to improve their abrasion resistance. Among the resins suggested for coating the high modulous yarns are acrylic resins, phenolic resins, and amino resins. The synthetic fiber to be coated or wrapped and then resin coated is a poly(paraphenylene terephthalamide). Among the materials disclosed for wrapping poly(para-phenylene terephthalamide) are asbestos, nylon, and Dacron.
Kahn, U.S. Pat. No. 4,259,394, discloses a base fabric which is utilized in conjunction with a needled batt to provide a paper machine felt. The needled fabric is subjected to a fusing operation which stabilizes the fabric and enhances the adhesion of the batt fibers to the base fabric as well as enhancing resistance of the fabric to compaction. The base fabric is composed of a core forming yarn wrapped with one or more layers of wrapping yarn. The core forming yarns are heat infusible and the wrapping yarns are heat fusible. The infusible yarns include aramid fibers, acrylic homopolymers, coated fiberglass, metallic fibers, and novoloid fibers. The fusible yarns include polyamide, polyester, olefin, and polyvinyl chloride. Also disclosed are yarns which have a core of polyester or nylon and are wrapped with polyethelene or polypropylene yarns. None of the above disclosed yarns provide the required abrasion resistance to meet the needs of the current industry standards. Accordingly, a need has continued to exist for a batt-on-mesh papermakers' felt, the abrasion resistance of which is superior to the prior art mesh bases.